An aircraft landing gear generally includes a shock absorber arranged to perform spring and damper functions. The shock absorber may contain hydraulic fluid, such as oil. An example of such a shock absorber is the “oleo-pneumatic” type, which combines oil and gas within a vessel to perform spring and damper functions.
For a fluid-containing shock absorber, the quantity of fluid present in the vessel is important in terms of ensuring the appropriate performance thereof. However, leakage and inappropriate servicing can lead to an inappropriate quantity of fluid in the vessel.
The present inventor has identified that a need exists for a means by which the appropriateness of the fluid level within such a shock absorber or other vessel can be determined in a manner which is one or more of: quick; simple; reliable; cheap to employ; and a low burden in terms of adding additional weight and/or complexity to the shock absorber.